Response of Bambara Groundnut (Vigna subterranea (l.) Verdc.) to Phosphorus Fertilisation in Botswana

Abstract

Soils in Botswana are known to be poor in phosphorus. Information is lacking on the P requirements of bambara groundnut (Vigna subterranea) in Botswana soils and soil moisture can also limit P uptake. Elsewhere the response of bambara groundnut to P fertilization is contradictory. The effects of phosphorus (P) fertilization on growth and yield of bambara groundnut were studied in a pot and a field experiments using a low P loamy sand (P-Bray 6.2 mg P kg-1) at Sebele Botswana. In the pot experiment, the response to two bambara groundnut landraces ('Diphiri Cream' and 'Zimbabwe Red') to P fertilization (0-480 mg P pot-1) was investigated. In the field experiment, the response of 'Diphiri Cream' to P fertilization (0-80 kg P ha-1) was investigated under two different soil moisture regimes (unsupplemented rainfall and supplementary irrigation) with samples taken at 28, 49,78, 99, days after sowing (DAS) and the final harvest at 126 DAS. In the pot experiment, terminated at 51 DAS, there was a positive response of shoot dry matter (DM) to P fertilization while the two landraces did not differ significantly. Root DM, nodule fresh weight and shoot P and nitrogen (N) concentrations were not affected by P fertilization. In the field, P fertilization had no effect, while supplementary irrigation increased all plant growth parameters except root DM. Total seed yield was 2.8 t and 4.2 t ha-1 for unsupplemented rainfall and supplementary irrigation treatments, respectively. Shoot P and N concentrations were not affected by soil moisture level. The positive effect of P in the pot and not in the field experiment may be an indication of low P supply of plants in pots due to a small rooted soil volume. The response in the pot experiment may indicate a 'starter P effect', whereas lack of response in the field may indicate unavailability of applied P to bambara groundnut. These aspects are discussed in this paper.

UNISWA Research Journal of Agriculture, Science and Technology Vol. 4 (2) 2000: pp 202-207